The purple hall is only designated as a dealer hall for the actual TCA meet. Since Monday,Tuesday and Wednesday are not part of the official show they might be treating those days differently and you may not need a tax number to sell. I haven’t seen it stated one way or the other.
On their FaceBook posts, they state that you need a tax number. Here in the "Peoples Republic of Pennsylvania", to sell at any public venue (like flea markets or dealer halls open to the public) a vendor is supposed to have a sales tax number and collect and remit sales taxes to the state. Some flea markets do not check the status of their vendors, so vendors there without the tax number could get some big state-induced headaches if they get a visit from a tax agent. It really all but killed off flea markets in the state which used to be abundant and a fun way to spend a Summer weekend . Here is a quick word from the horse's mouth.
I doubt that the EDTCA will allow anyone without a tax number due to their agreement with the Empire to keep the tax agents out of the member halls (and this is also why the member halls will never be open to the public). Other flea markets do not have such worries (and in the case of the hotels, have big corporations with armies of lawyers and lobbyists behind them), and they won't get in trouble if the tax man finds non-compliance within the ranks of their vendors.
Andy